Hi,
Nicholas Ellis and Margaret Plested married at Westminster: St Margaret on 10 Jan 1602.
The Nicholas Ellis who was born in 1578 was baptised 25th July 1578 at Saint Mary Matfelon, Stepney, Middlesex (Whitechapel - about 4-ish miles away from Saint Mary Matfelon).
If this is the correct son John then he was baptised at St Mary Matfelon on 2 Jul 1609 but there was also an original John baptised to a Nicholas Ellis on 16 Aug 1601 too. A daughter to Nicholas - Elizabeth was baptised at the same church 4 Sep 1608 and a son Abraham in 8 Feb 1606.
John Ellis married Sybil Craddock 25 Jan 1632 at London Saint Botolph's Aldgate, Middlesex
and that's all I've been able to find on Nicholas and John, sorry!
You might have more luck searching the siblings of Nicholas Ellis - for example, a Thomas Ellis was baptised 2 Aug 1575 at St Mary Matfelon, father's name "Ellis" (no other detail given), a Lucretia baptised same place and same father's name 28 May 1588, Hester in 1582, Elizabeth in 1582, Sara in 1588, Emmerie in 1587 might all provide more clues if you don't already have them..